Black Box Explains...Digital Visual Interface (DVI) and other digital display interfaces.
There are three main types of digital video interfaces: P&D, DFP, and DVI. P&D (Plug & Display, also known as EVC), the earliest of these technologies, supports both digital and... more/see it nowanalog RGB connections and is now used primarily on projectors. DFP (Digital Flat-Panel Port) was the first digital-only connector on displays and graphics cards; it’s being phased out.
There are different types of DVI connectors: DVI-D, DVI-I, DVI-A, DFP, and EVC.
DVI-D is a digital-only connector. DVI-I supports both digital and analog RGB connections. Some manufacturers are offering the DVI-I connector type on their products instead of separate analog and digital connectors. DVI-A is used to carry an analog DVI signal to a VGA device, such as a display. DFP, like DVI-D, was an early digital-only connector used on some displays; it’s being phased out. EVC (also known as P&D) is similar to DVI-I only it’s slightly larger in size. It also handles digital and analog connections, and it’s used primarily on projectors.
All these standards are based on transition-minimized differential signaling (TMDS). In a typical single-line digital signal, voltage is raised to a high level and decreased to a low level to create transitions that convey data. TMDS uses a pair of signal wires to minimize the number of transitions needed to transfer data. When one wire goes to a high-voltage state, the other goes to a low-voltage state. This balance increases the data-transfer rate and improves accuracy. collapse
Black Box Explains...Digital Visual Interface (DVI) and other digital display interfaces.
There are three main types of digital video interfaces: P&D, DFP, and DVI. P&D (Plug & Display, also known as EVC), the earliest of these technologies, supports both digital and analog RGB connections and is now used primarily on projectors. DFP (Digital Flat-Panel Port) was the first digital-only connector on displays and graphics cards; it’s being phased out.
There are different types of DVI connectors: DVI-D, DVI-I, DVI-A, DFP, and EVC.
DVI-D is a digital-only connector. DVI-I supports both digital and analog RGB connections. Some manufacturers are offering the DVI-I connector type on their products instead of separate analog and digital connectors. DVI-A is used to carry an analog DVI signal to a VGA device, such as a display. DFP, like DVI-D, was an early digital-only connector used on some displays; it’s being phased out. EVC (also known as P&D) is similar to DVI-I only it’s slightly larger in size. It also handles digital and analog connections, and it’s used primarily on projectors.
All these standards are based on transition-minimized differential signaling (TMDS). In a typical single-line digital signal, voltage is raised to a high level and decreased to a low level to create transitions that convey data. TMDS uses a pair of signal wires to minimize the number of transitions needed to transfer data. When one wire goes to a high-voltage state, the other goes to a low-voltage state. This balance increases the data-transfer rate and improves accuracy.
Black Box Explains...Component video.
Traditional Composite video standards—NTSC, PAL, or SECAM—combine luminance (brightness), chrominance (color), blanking pulses, sync pulses, and color burst information into a single signal.
Another video standard—S-Video—separates luminance from chrominance to provide... more/see it nowsome improvement in video quality.
But there’s a new kind of video called Component video appearing in many high-end video devices such as TVs and DVD players. Component video is an advanced digital format that separates chrominance, luminance, and synchronization into separate signals. It provides images with higher resolution and better color quality than either traditional Composite video or S-Video. There are two kinds of Component video: Y-Cb-Cr and Y-Pb-Pr. Y-Cb-Cr is often used by high-end DVD players. HDTV decoders typically use the Y-Pb-Pr Component video signal.
Many of today’s high-end video devices such as plasma televisions and DVD players actually have three sets of video connectors: Composite, S-Video, and Component. The easiest way to improve picture quality on your high-end TV is to simply connect it using the Component video connectors rather than the Composite or S-Video connectors. Using the Component video connection enables your TV to make use of the full range of video signals provided by your DVD player or cable box, giving you a sharper image and truer colors.
To use the Component video built into your video devices, all you need is the right cable. A Component video cable has three color-coded BNC connections at each end. For best image quality, choose a high-quality cable with adequate shielding and gold-plated connectors. collapse
Black Box Explains...Component video.
Traditional Composite video standards—NTSC, PAL, or SECAM—combine luminance (brightness), chrominance (color), blanking pulses, sync pulses, and color burst information into a single signal.
Another video standard—S-Video—separates luminance from chrominance to provide some improvement in video quality.
But there’s a new kind of video called Component video appearing in many high-end video devices such as TVs and DVD players. Component video is an advanced digital format that separates chrominance, luminance, and synchronization into separate signals. It provides images with higher resolution and better color quality than either traditional Composite video or S-Video. There are two kinds of Component video: Y-Cb-Cr and Y-Pb-Pr. Y-Cb-Cr is often used by high-end DVD players. HDTV decoders typically use the Y-Pb-Pr Component video signal.
Many of today’s high-end video devices such as plasma televisions and DVD players actually have three sets of video connectors: Composite, S-Video, and Component. The easiest way to improve picture quality on your high-end TV is to simply connect it using the Component video connectors rather than the Composite or S-Video connectors. Using the Component video connection enables your TV to make use of the full range of video signals provided by your DVD player or cable box, giving you a sharper image and truer colors.
To use the Component video built into your video devices, all you need is the right cable. A Component video cable has three color-coded BNC connections at each end. For best image quality, choose a high-quality cable with adequate shielding and gold-plated connectors.
Black Box Explains... How Autocross conversion can work for you.
When using media converters with 10BASE-T or 100BASE-TX cable, you may need to connect your converter to a non-hub device such as a PC or printer.
According to IEEE 802.3 Ethernet... more/see it nowstandards, media converters originally needed a specially pinned crossover cable to connect to PCs. The crossover cable matches the devices’ transmit and receive pins. Now there are media converters that use straight-pinned 10BASE-T patch cable but incorporate an uplink or crossover connection—a switch on the converter that’s set to support the PC-to-converter connection. By setting the uplink switch to “cross,” the converter’s internal mechanism crosses the pins on the RJ-45 connector to simulate a crossover cable.
Autocross conversion eliminates both the need to crosspin cables and set an uplink switch. It adapts to the pin assignment of the twisted-pair cable whether it’s crossed or uncrossed. And because it senses the pin configuration of any cable pinned to Ethernet specifications, it adjusts automatically without user configuration. collapse
Black Box Explains... How Autocross conversion can work for you.
When using media converters with 10BASE-T or 100BASE-TX cable, you may need to connect your converter to a non-hub device such as a PC or printer.
According to IEEE 802.3 Ethernet standards, media converters originally needed a specially pinned crossover cable to connect to PCs. The crossover cable matches the devices’ transmit and receive pins. Now there are media converters that use straight-pinned 10BASE-T patch cable but incorporate an uplink or crossover connection—a switch on the converter that’s set to support the PC-to-converter connection. By setting the uplink switch to “cross,” the converter’s internal mechanism crosses the pins on the RJ-45 connector to simulate a crossover cable.
Autocross conversion eliminates both the need to crosspin cables and set an uplink switch. It adapts to the pin assignment of the twisted-pair cable whether it’s crossed or uncrossed. And because it senses the pin configuration of any cable pinned to Ethernet specifications, it adjusts automatically without user configuration.
Black Box Explains... Industrial modem benefits.
Not all modems shuttle data in air-conditioned, climate-controlled comfort. And modems that operate in cozy environments have absolutely no business being exposed to harsh industrial conditions or to the elements.
But... more/see it nowjust because you work in a rough-and-tumble place doesn’t mean you have to sacrifice the convenience of a good modem. Instead, you should opt for an industrial modem. There are many industrial modems built for various degrees of extremity.
Survivability depends on reliability.
Sure, standard modems give you access to data in remote sites or enable you to service equipment on the plant floor—and you can do all this from the convenience of your office. However, these benefits are only possible if your modem can continue to function in its environment. And since standard modems aren’t built for adverse conditions, they’re not going to be reliable.
No penalties for interference.
Electrical control equipment—such as motors, relays, compressors, and generators—emit electromagnetic interference (EMI) that can affect the performance and reliability of a standard telephone modem.
EMI is emitted through power lines, the RS-232 communications cable, or through the telephone line itself. The very means of data communication, cable, is often the worst enemy of the standard modems that use it.
An industrial modem, on the other hand, has filters and superior EMI immunity to protect itself and your data. If you build your electrical cabinets to UL® or CSA standards, remember that your modem must also conform to UL® standard 508.
They go to extremes.
Temperature is the biggest killer of electronic equipment in industrial environments. The heat generated by industrial equipment in sealed enclosures or where space is a premium can make the temperature as much as 50 °F higher than the surrounding environment.
So standard modems can’t take the heat. But what about being outdoors in the other extreme, cold weather? Well, standard modems can’t take the cold either.
If you install your equipment in remote outdoor locations, it must work on the coldest days— especially those cold days when you least want to get in the car and go to the site to repair a standard modem that froze up.
Whether they’re placed in manufacturing environments or the great outdoors, industrial modems get the data through when you need it. They go to extremes for you.
Heavy metal for all kinds of banging around.
Industrial modems are built with durable metal enclosures that protect circuitry in rough conditions and ward off signal-disrupting EMI. Plus, they feature steel-bolt flanges to anchor them. In short, industrial modems can take the physical, heavy-duty punishment thrown their way.
So where exactly can you use an industrial modem?
• Heavy industry and manufacturing
• Oil and gas fields
• Refineries
• Storage sites
• Utility substations
• Agricultural projects
• Military facilities
• Research installations
• Water/wastewater systems
…and another thing!
If dedicated copper lines can’t be run through industrial environments, or if the fiber optic option is cost-prohibitive, there are also wireless industrial modems that make line-of-sight connections. If there’s a way to get the data through, industrial modems will get the job done.
Industrial-strength assurance.
Industrial modems remain in service for a very long time. But if you ever need a replacement that is hardware or software compatible, be assured that Black Box continues to support its products year after year—so you don’t spend your time re-engineering systems if you have to make a replacement. collapse
Black Box Explains... Industrial modem benefits.
Not all modems shuttle data in air-conditioned, climate-controlled comfort. And modems that operate in cozy environments have absolutely no business being exposed to harsh industrial conditions or to the elements.
But just because you work in a rough-and-tumble place doesn’t mean you have to sacrifice the convenience of a good modem. Instead, you should opt for an industrial modem. There are many industrial modems built for various degrees of extremity.
Survivability depends on reliability.
Sure, standard modems give you access to data in remote sites or enable you to service equipment on the plant floor—and you can do all this from the convenience of your office. However, these benefits are only possible if your modem can continue to function in its environment. And since standard modems aren’t built for adverse conditions, they’re not going to be reliable.
No penalties for interference.
Electrical control equipment—such as motors, relays, compressors, and generators—emit electromagnetic interference (EMI) that can affect the performance and reliability of a standard telephone modem.
EMI is emitted through power lines, the RS-232 communications cable, or through the telephone line itself. The very means of data communication, cable, is often the worst enemy of the standard modems that use it.
An industrial modem, on the other hand, has filters and superior EMI immunity to protect itself and your data. If you build your electrical cabinets to UL® or CSA standards, remember that your modem must also conform to UL® standard 508.
They go to extremes.
Temperature is the biggest killer of electronic equipment in industrial environments. The heat generated by industrial equipment in sealed enclosures or where space is a premium can make the temperature as much as 50 °F higher than the surrounding environment.
So standard modems can’t take the heat. But what about being outdoors in the other extreme, cold weather? Well, standard modems can’t take the cold either.
If you install your equipment in remote outdoor locations, it must work on the coldest days— especially those cold days when you least want to get in the car and go to the site to repair a standard modem that froze up.
Whether they’re placed in manufacturing environments or the great outdoors, industrial modems get the data through when you need it. They go to extremes for you.
Heavy metal for all kinds of banging around.
Industrial modems are built with durable metal enclosures that protect circuitry in rough conditions and ward off signal-disrupting EMI. Plus, they feature steel-bolt flanges to anchor them. In short, industrial modems can take the physical, heavy-duty punishment thrown their way.
So where exactly can you use an industrial modem?
• Heavy industry and manufacturing
• Oil and gas fields
• Refineries
• Storage sites
• Utility substations
• Agricultural projects
• Military facilities
• Research installations
• Water/wastewater systems
…and another thing!
If dedicated copper lines can’t be run through industrial environments, or if the fiber optic option is cost-prohibitive, there are also wireless industrial modems that make line-of-sight connections. If there’s a way to get the data through, industrial modems will get the job done.
Industrial-strength assurance.
Industrial modems remain in service for a very long time. But if you ever need a replacement that is hardware or software compatible, be assured that Black Box continues to support its products year after year—so you don’t spend your time re-engineering systems if you have to make a replacement.
Black Box Explains...FDDI
Fiber Distributed Data Interface (FDDI) is a networking standard for operating at speeds of up to 100 Mbps. The standard FDDI network is set up in a ring topology with... more/see it nowtwo rings that transmit signals in opposite directions to a series of nodes. FDDI accommodates up to 500 nodes per dual-ring network with spacing up to 2 kilometers between adjacent nodes. FDDI uses the same token-passing scheme as the IEEE 802.5 Token Ring network to control transmission around the loop. collapse
Black Box Explains...FDDI
Fiber Distributed Data Interface (FDDI) is a networking standard for operating at speeds of up to 100 Mbps. The standard FDDI network is set up in a ring topology with two rings that transmit signals in opposite directions to a series of nodes. FDDI accommodates up to 500 nodes per dual-ring network with spacing up to 2 kilometers between adjacent nodes. FDDI uses the same token-passing scheme as the IEEE 802.5 Token Ring network to control transmission around the loop.
Black Box Explains...USB.
The newest USB standard, USB 3.0 or “SuperSpeed USB”, provides vast improvements over USB 2.0. USB 3.0 promises speeds up to 4.8 Gbps, nearly ten times that of USB 2.0.... more/see it nowUSB 3.0 adds a physical bus running in parallel with the existing 2.0 bus. It has the flat USB Type A plug, but inside there is an extra set of connectors and the edge of the plug is blue instead of white. The Type B plug looks different with an extra set of connectors.
The USB 3.0 cable contains nine wires, four more than USB 2.0, which has one pair for data and one pair for power. USB 3.0 adds two more data pairs, for a total of eight plus a ground. These extra pairs enable USB 3.0 to support bidirectional asynchronous, full-duplex data transfer instead of USB 2.0's half-duplex pollling method. USB 3.0 also provides 50% more power than USB 2.0 (150 mA vs 100 mA) to unconfigured devices and up to 80% more power (900 mA vs 500 mA) to configured devices. It also conserves power too compared to USB 2.0, which uses power when the cable isn’t being used. collapse
Black Box Explains...USB.
The newest USB standard, USB 3.0 or “SuperSpeed USB”, provides vast improvements over USB 2.0. USB 3.0 promises speeds up to 4.8 Gbps, nearly ten times that of USB 2.0. USB 3.0 adds a physical bus running in parallel with the existing 2.0 bus. It has the flat USB Type A plug, but inside there is an extra set of connectors and the edge of the plug is blue instead of white. The Type B plug looks different with an extra set of connectors.
The USB 3.0 cable contains nine wires, four more than USB 2.0, which has one pair for data and one pair for power. USB 3.0 adds two more data pairs, for a total of eight plus a ground. These extra pairs enable USB 3.0 to support bidirectional asynchronous, full-duplex data transfer instead of USB 2.0's half-duplex pollling method. USB 3.0 also provides 50% more power than USB 2.0 (150 mA vs 100 mA) to unconfigured devices and up to 80% more power (900 mA vs 500 mA) to configured devices. It also conserves power too compared to USB 2.0, which uses power when the cable isn’t being used.
Black Box Explains...Rack units.
A Rack Unit is abbreviated as U. One Rack Unit (1U) is equal to 1.75" (4.44 cm).
Black Box Explains…Network Time Protocol (NTP).
Network Time Protocol (NTP) dates to the early 1980s and is one of the oldest protocols used on the Internet today. NTP was developed to synchronize a network through the... more/see it nowuse of NTP servers and latency compensation to ensure that every device on a network shows the correct time.
NTP is based on a hierarchical system of clocks and NTP servers. At the top of the hierarchy are clock sources such as atomic or GPS clocks. These clocks are referred to as Stratum 0. NTP servers connected directly to a clock source are referred to as Stratum 1, servers connected to Stratum 1 servers are called Stratum 2, and so on.
Many Stratum 1 NTP servers—often called just time servers—are available for reference on the Internet. The National Institute of Standards and Technology (NIST) Internet Time Service provides many of these servers. Generally, servers closer to the clock—Stratum 1 and Stratum 2—are considered to be more accurate than servers further from the clock. NTP provides Coordinated Universal Time (UTC), which is based on International Atomic Time (TAI), and has support for leap seconds.
To set the correct time, a client device polls several NTP servers, throws out any times that appear to be anomalous, and averages the remaining times to come up with a best estimate of the correct time. An NTP transaction consists of four timestamps:
A client timestamp when a request is sent to the server.
A server timestamp when the request is received by the server.
A server timestamp when the reply is sent to the client.
A client timestamp when the reply is received by the client.
The client device uses these timestamps to compensate for latency and calculate the correct time. Accuracy can usually be maintained within a few milliseconds, even over the Internet.
A compatible standard, Simple Network Time Protocol (SNTP), polls only one NTP server to obtain the time.
Most of today’s computer operating systems include support for NTP or SNTP. Most managers of large networks set up a Stratum 2 NTP server and have computers on the network get their time from that server using SNTP. Having one NTP server for the network rather than having each device going to outside servers for the time ensures accurate and consistent time across the network.
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Black Box Explains…Network Time Protocol (NTP).
Network Time Protocol (NTP) dates to the early 1980s and is one of the oldest protocols used on the Internet today. NTP was developed to synchronize a network through the use of NTP servers and latency compensation to ensure that every device on a network shows the correct time.
NTP is based on a hierarchical system of clocks and NTP servers. At the top of the hierarchy are clock sources such as atomic or GPS clocks. These clocks are referred to as Stratum 0. NTP servers connected directly to a clock source are referred to as Stratum 1, servers connected to Stratum 1 servers are called Stratum 2, and so on.
Many Stratum 1 NTP servers—often called just time servers—are available for reference on the Internet. The National Institute of Standards and Technology (NIST) Internet Time Service provides many of these servers. Generally, servers closer to the clock—Stratum 1 and Stratum 2—are considered to be more accurate than servers further from the clock. NTP provides Coordinated Universal Time (UTC), which is based on International Atomic Time (TAI), and has support for leap seconds.
To set the correct time, a client device polls several NTP servers, throws out any times that appear to be anomalous, and averages the remaining times to come up with a best estimate of the correct time. An NTP transaction consists of four timestamps:
A client timestamp when a request is sent to the server.
A server timestamp when the request is received by the server.
A server timestamp when the reply is sent to the client.
A client timestamp when the reply is received by the client.
The client device uses these timestamps to compensate for latency and calculate the correct time. Accuracy can usually be maintained within a few milliseconds, even over the Internet.
A compatible standard, Simple Network Time Protocol (SNTP), polls only one NTP server to obtain the time.
Most of today’s computer operating systems include support for NTP or SNTP. Most managers of large networks set up a Stratum 2 NTP server and have computers on the network get their time from that server using SNTP. Having one NTP server for the network rather than having each device going to outside servers for the time ensures accurate and consistent time across the network.
Black Box Explains...Coax connectors.
The BNC (Bayonet-Neill-Concelman) connector is the most commonly used coax connector. This large ”bayonet“ connector features a slotted outer conductor and an inner plastic dielectric, and it offers easy connection... more/see it nowand disconnection. After insertion, the plug is turned, tightening the pins in the socket. It is widely used in video and Radio Frequency (RF) applications up to 2.4 GHz. It is also common in 10BASE2 Ethernet networks, on cable interconnections, network cards, and test equipment.
The TNC connector is a threaded version of the BNC connector. It works in frequencies up to 12 GHz. It‘s commonly used in cellular telephone RF/antenna applications.
The N connector is a larger, threaded connector that was designed in the 1940s for military systems operating at less than 5 GHz. In the 1960s, improvements raised performance to 12 GHz. The connector features an internal gasket and is hand tightened. It is common on 2.4-GHz antennas.
The UHF connector looks like a coarse-threaded, big center-conductor version of the N connector. It was developed in the 1930s. It is suitable for use up to 200–300 MHz and generally offers nonconstant impedance.
The F connector is most often used in cable and satellite TV and antenna applications; and it performs well at high frequencies. The connector has a 3/8–32 coupling thread. Some F connectors are also available in a screw-on style.
The SMA (Subminiature A) connector is one of the most common RF/microwave connectors. This small, threaded connector is used on small cables that won’t be connected and disconnected often. It’s designed for use to 12.4 GHz, but works well at 18, and sometimes even up to 24 GHz. This connector is often used in avionics, radar, and microwave communications.
The SMC (Subminiature C) connector is a small, screw-on version of the SMA. It uses a 10–32 threaded interface and can be used in frequencies up to 10 GHz. This connector is used primarily in microwave environments.
The SMB (Subminiature B) connector is a small version of the SMC connector. It was developed in the 1960s and features a snap-on coupling for fast connections. It features a self-centering outer spring and overlapping dielectric. It is rated from 2–4 GHZ, but can possibly work up to 10 GHz.
The MCX (Micro Coax) connector is a coax RF connector developed in the 1980s. It has a snap-on interface and uses the same inner contact and insulator as the SMB connector but is 30% smaller. It can be used in broadband applications up to 6 GHz.
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Black Box Explains...Coax connectors.
The BNC (Bayonet-Neill-Concelman) connector is the most commonly used coax connector. This large ”bayonet“ connector features a slotted outer conductor and an inner plastic dielectric, and it offers easy connection and disconnection. After insertion, the plug is turned, tightening the pins in the socket. It is widely used in video and Radio Frequency (RF) applications up to 2.4 GHz. It is also common in 10BASE2 Ethernet networks, on cable interconnections, network cards, and test equipment.
The TNC connector is a threaded version of the BNC connector. It works in frequencies up to 12 GHz. It‘s commonly used in cellular telephone RF/antenna applications.
The N connector is a larger, threaded connector that was designed in the 1940s for military systems operating at less than 5 GHz. In the 1960s, improvements raised performance to 12 GHz. The connector features an internal gasket and is hand tightened. It is common on 2.4-GHz antennas.
The UHF connector looks like a coarse-threaded, big center-conductor version of the N connector. It was developed in the 1930s. It is suitable for use up to 200–300 MHz and generally offers nonconstant impedance.
The F connector is most often used in cable and satellite TV and antenna applications; and it performs well at high frequencies. The connector has a 3/8–32 coupling thread. Some F connectors are also available in a screw-on style.
The SMA (Subminiature A) connector is one of the most common RF/microwave connectors. This small, threaded connector is used on small cables that won’t be connected and disconnected often. It’s designed for use to 12.4 GHz, but works well at 18, and sometimes even up to 24 GHz. This connector is often used in avionics, radar, and microwave communications.
The SMC (Subminiature C) connector is a small, screw-on version of the SMA. It uses a 10–32 threaded interface and can be used in frequencies up to 10 GHz. This connector is used primarily in microwave environments.
The SMB (Subminiature B) connector is a small version of the SMC connector. It was developed in the 1960s and features a snap-on coupling for fast connections. It features a self-centering outer spring and overlapping dielectric. It is rated from 2–4 GHZ, but can possibly work up to 10 GHz.
The MCX (Micro Coax) connector is a coax RF connector developed in the 1980s. It has a snap-on interface and uses the same inner contact and insulator as the SMB connector but is 30% smaller. It can be used in broadband applications up to 6 GHz.
Black Box Explains...RS-232.
RS-232, also known as RS-232C and TIA/EIA-232-E, is a group of electrical, functional, and mechanical specifications for serial interfaces between computers, terminals, and peripherals. The RS-232 standard was developed by... more/see it nowthe Electrical Industries Association (EIA), and defines requirements for connecting data communications equipment (DCE)—modems, converters, etc.—and data terminal equipment (DTE)—computers, controllers, etc.) devices. RS-232 transmits data at speeds up to 115 Kbps and over distances up to 50 feet (15.2 m).
The standard, which is functionally equivalent to ITU V.24/V.28, specifies the workings of the interface, circuitry, and connector pinning. Both sync and async binary data transmission fall under RS-232. Although RS-232 is sometimes still used to transmit data from PCs to peripheral devices, the most common uses today are for network console ports and for industrial devices.
Even though RS-232 is a “standard,” you can’t necessarily expect seamless communication between two RS-232 devices. Why? Because different devices have different circuitry or pinning, and different wires may be designated to perform different functions.
The typical RS-232 connector is DB25, but some PCs and other data communication devices have DB9 connectors and many newer devices have RJ-45 RS-232 ports. To connect 9-pin PC ports or RJ-45 to devices with 25-pin connectors, you will require a simple adapter cable. collapse
Black Box Explains...RS-232.
RS-232, also known as RS-232C and TIA/EIA-232-E, is a group of electrical, functional, and mechanical specifications for serial interfaces between computers, terminals, and peripherals. The RS-232 standard was developed by the Electrical Industries Association (EIA), and defines requirements for connecting data communications equipment (DCE)—modems, converters, etc.—and data terminal equipment (DTE)—computers, controllers, etc.) devices. RS-232 transmits data at speeds up to 115 Kbps and over distances up to 50 feet (15.2 m).
The standard, which is functionally equivalent to ITU V.24/V.28, specifies the workings of the interface, circuitry, and connector pinning. Both sync and async binary data transmission fall under RS-232. Although RS-232 is sometimes still used to transmit data from PCs to peripheral devices, the most common uses today are for network console ports and for industrial devices.
Even though RS-232 is a “standard,” you can’t necessarily expect seamless communication between two RS-232 devices. Why? Because different devices have different circuitry or pinning, and different wires may be designated to perform different functions.
The typical RS-232 connector is DB25, but some PCs and other data communication devices have DB9 connectors and many newer devices have RJ-45 RS-232 ports. To connect 9-pin PC ports or RJ-45 to devices with 25-pin connectors, you will require a simple adapter cable.